1. Field of the Invention
The present invention relates to a channel baler including a pressure channel, a plunger located in the pressure channel, and a thrust crank drive for displacing the plunger in the pressure channel.
2. Description of the Prior Art
It is generally known to provide means for protecting a baler drive from an overload. Such means, for example, as used in a big baler "Quadrant 1200" of the "Claas" type. When the pressure plunger applies too large a force, bending of a crossbar of the drive suspension by several mm results in the opening of a four-way directional control valve which leads to a reduction of hydraulic pressure in the hydraulic cylinders responsible for tensioning the pressure channel. Upon release of the baler, the predetermined pressure is restored.
In addition, between the main drive and the drive gear, shearing protection means is provided. The drawback of this arrangement consists in that the reduction in the resistance of the compressed mass, as a result of movement of the side wall of the pressure channel, takes place rather slowly for the required reduction of the density. A further drawback consists in that, e.g., the formation of large compressed packages or bales from moist products results in actuation of the shearing protection means at the last strokes. This leads to stoppage of the baler.
German Publication DE 92 06 232 discloses a large baler in which between the drive gear and the main drive, there is provided means for an automatic breaking and restoration of the drive chain. The response torque of the coupling should be adjusted very precisely, otherwise the coupling would respond too quickly at a low overload or too slowly at a large overload.
U.S. Pat. No. 4,565,123 discloses a channel baler with a hydraulic drive for the plunger. In addition, the channel baler of U.S. Pat. No. 4,565,123 includes a tension mechanism associated with the pressure channel. When a predetermined pressure in the pressure channel is exceeded, a pressure switch in the hydraulic circuit of the plunger is actuated and causes movement of a valve in the hydraulic circuit of the tension device into the open position of the valve. Thereby, the cross-section of the pressure channel is increased, and blocking of the plunger is prevented. With a free displacement of the plunger, the pressure in the hydraulic circuit of the tension device is automatically restored. There is also provided a pressure-limiting valve for protection from overload and which interrupts the drive upon an occurrence of an overload.
U.S. Pat. No. 3,350,999 discloses a baler including a device which at an end of each bale-forming stroke, releases the baler outlet by releasing, for a short time, the tension mechanism provided at the outlet of the pressure channel. Thereby, blocking of a bale, which is displaced by a newly-formed bale, is prevented. When the hydraulic pressure in the hydraulic circuit of the plunger exceeds a pre-determined value, the pressure in the hydraulic cylinder of the tension device is reduced automatically, and a compressed coil spring, which forms part of the tension device, releases the pressure channel outlet. The device disclosed in U.S. Pat. No. 3,350,999 permits to reduce power consumption which is required for releasing the tension device, and which depends on the pressure forces acting in the pressure channel. A drawback of the device consists in a relatively slow response of the device to increase and decrease of the pressure in the pressure channel.
Further, this arrangement is not suitable for balers with a mechanical thrust crank drive. A further drawback consists in that the bale density is diminished because of a relatively long time during which the pressure channel remains open. The relatively long time, during which the pressure channel remains open, results from a need to release all of the walls of the channel to achieve a desired effect.
European Patent Publication EP 0 235 397 B1 discloses a device for controlling the width of the pressure channel dependent on resistance to the displacement of bales which is caused by friction between the bales and channel walls, resulting from the movement of the bales through the channel. The retaining force of a sliding rail of the pressure channel is determined by a hydraulic cylinder which is provided between the frame of the baler and the sliding rail, and which is used for controlling the position of the slide rail.
Controlling the position of the slide rail permits to achieve a most possible constant compressed density of the rails. Here, likewise, additional overload protection means is provided between the drive gear and the main drive for interrupting force transmission in case of an overload.
Accordingly, an object of the present invention is a channel baler of the above-described type in which the loading peaks of the baler during the bale-forming step are rapidly eliminated without the interruption of force transmission.
Another object of the present invention is achieving high compressed densities without blocking of bale-forming and delivery elements.